A vitamin D.sub.3 analog III, is currently under evaluation for the treatment of osteoporosis. The existing preparation, described in European Patent Application EP 808833, relies on the Lythgoe phosphine oxide approach, in which CD-ring fragment I is coupled with A-ring fragment II, followed by deprotection of the product to give III. ##STR1##
The present invention provides a process for the preparation of a novel triethylsilyl ether analog of the CD ring fragment, compound 8, as outlined in the following Reaction Scheme. ##STR2##
Compound 3, used in the above scheme, may be synthesized according to the following scheme: ##STR3##
The present invention provides a compound having the formula ##STR4##
wherein R.sub.1 is a lower alkyl group. The present invention also provided a compound having the formula ##STR5##
wherein R.sub.1 is a lower alkyl group and R.sub.2 is a silyl protecting group. The invention further provides a compound having the formula ##STR6##
wherein R.sub.1 is a silyl protecting group. The invention further provides a compound having the formula ##STR7##
wherein R.sub.1 is p-toluenesulfonyl, benzenesulfonyl, methanesulfonyl; and R.sub.2 is a silyl protecting group.
The invention also provides a process for producing each of the compounds set forth above.